Sliding doors such as ones providing egress, for example, from a residential dwelling to a patio or deck are well-known in the prior art. Such prior art is fairly well developed. Sliding doors having been in existence for a considerable period of time. Typically, such doors, which are known as French doors, are utilized to provide access, as indicated above, to patios, decks, etc. from residences with which such patios, decks, etc. are associated.
Of serious concern in the manufacture of doors in general and, particularly, sliding doors, is the sill structure. The sill is the portion which provides the threshhold over which one passes when passing through the door closure.
In the case of sliding doors, sills provide unique problems. They must be resistent to chemical action which might result from exposure to ultraviolet light. Additionally, they must be strong and durable, since traffic across them can be quite significant.
In the prior art, various materials have been employed in the manufacture of sliding door sills. Wood is one particular composition which has been employed. Wood, however, decays over a period of time, since wood absorbs moisture. Even when decay is slow so that the useful life of a sill is obtained, warping can occur. Warping, if significant enough, can create a safety hazard. At a minimum, however, it gives rise to an unsightly condition.
Aluminum has been deemed to be a logical choice for a sliding door sill application. Aluminum has been thought to have the most significant strength for this application. Stronger materials would, of course, be more desirable.
Even aside from the strength issue, however, aluminum does have certain drawbacks. Because of its inherent metallic properties, aluminum has a relatively high coefficient of thermal conductivity. When used in a sliding door sill application, aluminum can conduct heat within the building in which the door is installed to the outside. This is a particularly acute problem in geographic locations where winters are very cold. In extreme temperature conditions, the temperature gradient between the inside and outside of a building is quite extreme.
The solution proposed when aluminum is used has been to provide a thermal break in order to inhibit thermal conduction. Doing this, however, has translated to high manufacturing costs.
It is to these dictates of the prior art and the problems discussed above that the present invention is directed. It is a composition for a sliding door sill which overcomes the problems of the prior art, taking into account the desirable dictates for such a product.